Throughout the passage of time and the shifts in backgrounds, a particular war continues to leave its mark on history, extending its influence into the modern world. There are two major groups involved in the ensuring war. The first group consists of monsters known as Chiropterans who can change their appearances into that of human beings. They are actually immortals who feed on the blood of the living. The second group is an organisation known as the "Red Shield", formed to track down these monsters and exterminate them. Otonashi Saya is a high-school girl who lives a peaceful life with her family. The only problem is, she has no recollections of her life beyond that of the past year. However, her happy life will be destroyed by an event that will lead her to her destined fate.
Saya leads a happy life with her adoptive parent, George, and brothers, Kai and Riku in Okinawa, Japan. She lost her memory and cannot remember anything beyond the past year of her life. After witnessing a creature kill a teacher at her school things automatically change. Now the monster is after her and the only one that can help her is a mysterious cellist. Now her true destiny begins to emerge and her life is changed forever.
After being kissed and being forced to drink blood, by the cellist, Saya's eyes begin to glow and she becomes a fighting machine. After easily slicing through the Chiropteran Saya collapses. She wakes in the hospital and hears George and David talking about her. Their conversation scares her so bad that she runs away. Now it is up to Kai to find her.
David has given George a deadline to hand over Saya back to the Red Shield. George takes Saya to his family grave to show what exactly happened to her one year ago.
George is taken into ICU after being severely injured. Angered, Kai takes the gun that George had been hiding and goes after Forrest. Riku informs Saya about Kai and both of them go off to search for Kai. Kai finds Forrest, but it seems he has become the monster he was when he attacked George. Now Saya must get to Kai as quickly as possible, for it is a matter of life and death. Can she get there is time?
David prepares his group to go after George. When they learn he has been secretly transfered to the Yanabaru laboratory in Northern Okinawa, they prepare to head there. When Kai finds out he decides he decides he want to go with the group. But will David allow it?
David, Saya, and Hagi infiltrate the Yanbaru laboratory to rescue George. While they are there David finds out the US army is artificially creating Chiropterans. Along with the information on the artificial Chriopterans, David finds the mysterious keyword "Delta 67". Meanwhile the Commander of US Forces on Okinawa has authorized surgical bombing of Yanbaru to remove any incriminating evidence.
While David and Julia decode what they found at Yanbaru, Riku finds out about George's death. After finding out, Riku hides in his room and refuses to come out. Now Kai must take on a fatherly role to cheer his brother up.
Saya is enrolled in a French school in Vietnam that was associated with the wine found at the military base, while Hagi goes undercover as a gardener. Not long after getting there Saya learns from her talkative roommate that the phantom at the school kidnaps girls that look similar to Saya. After investigating some more Saya is led to the bell tower where she comes face to face with the phantom.
Saya reports to Red Sheild that all the missing girls have similar looks to her. Meanwhile Riku meets a Vietnamese girl named Mui who has the same ability as him. After spending some time with Mui, Riku realizes the importance of his family and decides to try and reunite with Kai and Saya. The American military team makes it seem impossible when they kidnap Riku and Mui.
When Saya arrives in her class one morning, she finds a blue rose. With the blue rose in hand Saya and Haji go to the rose garden where the blue roses are said to bloom. After a little looking around they find a staircase leading underground in a shack. Is this where the phantom is hiding?
A ball is held once a year at the school and students and their parents arrive dressed in formal attire. Saya goes wearing a dress she borrowed from Min. While she is at the ball Saya meets a young man named Solomon. David and other people from Red Sheild show at the ball, but they are not the only strangers there. The Phantom appears and now Saya and everyone must do their best to defeat him.
Saya and the group, joined along by The Red Shield, Clara, Spencer, Rogers and McCoy, pursue the container carrying Diva which was transferred to the school. They trek up the Mekong River to the experiment farm of Cinq Fleche Pharmaceutical where they find Mui, Riku and Kai as well as numerous children kidnapped and brought here from all over Vietnam. Saya and the others are not aware of this fact, however, as they prepare for a clash.
Still held up at the experiment farm and surrounded by Chiropteran children, Saya soon hears mysterious humming and the roars of the Chiropterans. Eventually, the smell of blood becomes asphyxiating, and threatens to wrest control of herself from her.